The foundations of Sir Harry Ricardo’s career were laid when he helped professor Hopkinson with his research work at Cambridge, but he first became well known when he designed the outstandingly successful engine for tanks when they were first used in the 1914-18 war. After this war he investigated fuels for petrol engines, and this resulted in drastic changes in the refining and marketing policies of the Shell organisation,

He again contributed to his country’s victory in the 1939-45 war, because it is fair to say that the Bristol Aeroplane Co. founded their sleeve valve engine on Sir Harry’s work. Altogether, 130,000 sleeve valve aero engines have been built mostly by the Bristol and Napier companies.

He has also left his mark on diesel engines, as the well known Ricardo "Comet" combustion system has been built into engines all over the world by more than fifty licensees. Each year newly manufactured engines of this type produce an aggregate of 6,000,000 horse power (1965).

He was knighted in 1948 in recognition of his work in the field of internal combustion engineering and research.


(1) "Presidential Address", Institution of  Mechanical Engineers,  1944 (Proc. I. Mech. E., 152, 1945)

(2) "Horning Memorial Lecture, 1955" (Chartered Mechanical Engineer, September, 1955)

(3) Unpublished Technical Notes by Sir Harry Ricardo. (These notes subsequently formed the basis of his book:
Memories and Machines published by Constable in 1968.)


Work at Cambridge with Professor Hopkinson

At Cambridge I started working for the Mechanical Sciences Tripos, but after my first year, Professor Hopkinson invited me to assist him in some researches he was about to undertake into the internal combustion engine. Up to that time, I had taken no special interest in internal combustion engines as such, though the advent of the motor-car, then a fascinating but wayward mechanical toy, had, of course, thrilled me.

Under Hopkinson’s lead, my interest in and enthusiasm for the internal combustion engine, were thoroughly roused. Hopkinson was, I think, quite the most stimulating research leader I have ever met, with an almost uncanny perception combined with good judgement and a thoroughly practical out-look. Hopkinson’s methods were by no means always orthodox; he believed in following, step by step, a logical and reasoned sequence but only up to a point; if that looked like becoming too prolonged, then he would fall back on the principle of trying every bottle on the shelf, and if that did not achieve his end, his next step was to try something really silly and see what happened. He taught me never to accept anything at second-hand, unless it accorded with one’s own common sense and experience; to be sceptical of one’s own observations when they failed in this respect; and never to cling too long to a theory, however cherished.

Hopkinson’s first step was to design and develop a really efficient and reliable optical indicator, for he suspected - and rightly so - that many previous research workers had been misled by the vagaries of the orthodox pencil indicator. His design of this instrument was most ingenious, and the very first version we made in the workshops worked beautifully, after only very little detail development. With the help of this indicator, we started out to investigate the performance of a modern (1904) gas engine, and, in parallel, we carried out combustion experiments in closed vessels, as others had done before us. At once he drew my attention to the fact that the rate of burning of the same combustible mixture at the same temperature and pressure, was enormously more rapid in the engine cylinder than in the explosion vessel. He suggested that this might be due to the spreading of flame by turbulence in the engine cylinder and proposed that we should put inside the explosion vessel a small electric fan. This done, we found that the rate of burning could be speeded up enormously, and that nearly in proportion to the speed of the fan. By a coincidence, Sir Dugald Clerk, working quite independently, demonstrated the same thing at about the same time, but he reversed the process, for he motored an engine with all valves closed and ignition cut off in order to allow the turbulence to subside; he then switched on the ignition, when the rate of burning was found to be so slow as to be quite out of court even for a very slow-speed engine.

These two entirely independent observations were of first-rate importance, for they showed, for the first time, how vital a part turbulence plays in the functioning of an internal combustion engine.

Hopkinson had his eyes fixed always on the light high-speed engine as the internal combustion engine of the future, and prophesied that, given sufficient turbulence, there was no limit in sight to the speed at which an internal combustion engine could run, and run efficiently; and even today, no such limit is yet in sight.

We concentrated all our attention on exploring the limitations of that gas engine. We studded it with thermocouples and measured the temperature gradients through the cylinder walls and piston; we raised its compression till pre-ignition set in, we then water-cooled the exhaust valve and raised it yet again, all with the object of finding what factors set a limit to the power and efficiency obtainable. At that time, and with Cambridge gas, pre-ignition, that is to say, self-ignition in advance of the timed spark, proved to be one of the limiting factors, and Hopkinson set out to investigate this. For the purpose, he inserted into the cylinder through the breech end, a steel plug fitted with a thermocouple at its inner end. The farther the plug was projected into the cylinder, the hotter it became, until eventually it reached a temperature which ignited the working fluid before the passage of the spark. By projecting the plug farther into the cylinder, we could induce pre-ignition at any point in the compression stroke, and at the same time could observe the temperature at which it was initiated. We found, of course, that as premature ignition set in, the power fell off, accompanied by a dull thumping, due to reversal of load on the connecting rod bearings; but as the ignition grew earlier, the thumping ceased and eventually the engine, running quite smoothly, came gently to a standstill. Our indicator diagrams showed no change in rate of pressure rise, nor did the conditions differ in any way from those which obtained when we over-advanced the spark ignition. None of these findings were in the least surprising - I mention them only in view of what I am going to say about the petrol engine.

The petrol engine of that date, and indeed of today for that matter, had a habit of knocking sharply under certain conditions. This knocking was popularly, and indeed universally, attributed to premature ignition, brought about by some over-heated surface inside the cylinder. The knock in the petrol engine was, however, a high-pitched ringing noise, quite unlike the dull thud produced by premature ignition in the gas engine. During my last year at Cambridge, 1906, we managed to borrow a four-cylinder high-speed petrol engine of the most up-to-date design, and this also Hopkinson put through an equally critical examination. We applied his optical indicator and found that we could get really excellent indicator diagrams at speeds up to 1, 200 r.p.m. Under certain conditions, when running on a weak mixture, for example, or with wide open throttle at low speeds, this engine would knock in the most alarming manner. We tried hard to secure indicator diagrams under knocking conditions, but without success, for every time a knock occurred in the cylinder we were indicating, the mirror of the indicator was either shot out of its frame or shattered, a thing which had never occurred when indicating the gas engine. Hopkinson was very puzzled and intrigued by this and, with his usual quick perception, he attributed it to the setting up of an explosion wave inside the combustion chamber, a wave whose impact was sufficient both to shatter the indicator mirror and to set the cylinder walls in vibration, thus causing the high-pitched ‘ping". Since the same phenomena could not be reproduced in the gas engine, he suggested that this "detonation", as he called it, must be a characteristic of the fuel. He would have liked to have investigated the question further, but the engine had to be returned to its owner and there, for the time being, the matter ended.

While working with Hopkinson, I had designed and built in the University Workshops, a two-stroke cycle engine in which I had sought to apply, as far as possible, the lessons of our research. In this engine I tried to combine a high degree of turbulence with the use of a stratified charge, in order to enable me to run at high speed and over a very wide range of mixture strength. In this rather ambitious project, I was partially successful.

Extract from "Presidential Address" (Ref. 1)

"In retrospect I am amazed at the ground Hopkinson covered in so short a time and at his ingenuity in devising very simple but convincing experiments, involving the absolute minimum of equipment. His lectures and administrative duties left him very little time, and there was no grant of money for research; I, too, had to attend lectures and work for my degree, yet we were never in a hurry, we certainly never burned the midnight oil or missed a single meal or entertainment.

The secret, I think, was to be found in two important factors. Firstly there was no telephone in the laboratory, and secondly our instrumentation was of the simplest possible kind which could be checked and calibrated in a few minutes and relied upon with confidence. Today I arm appalled by the amount of time spent in setting up, calibrating and correcting the very elaborate instrumentation upon which we are daily becoming more dependent."

Extract from "Horning Memorial Lecture, 1955" (Ref. 2)


The design and development of this engine was one of Sir Harry Ricardo’s first commercial ventures:

"I designed and built in the workshops at Cambridge the first version while I was an undergraduate in 1903-04. This gave quite a promising performance. I then designed and built, also in the workshops at Cambridge, an improved version, which was completed in 1905 and was put through fairly thorough calibration tests in the engineering laboratory. After leaving Cambridge I experimented a good deal in my own small workshop with this engine in my own spare time."

A small firm, Messrs Lloyd and Plaister, became interested in the engine and Ricardo designed two sizes of the engine for a small and a large car. The small model was a fair success, about 50 being produced before the death of Mr. Lloyd and the outbreak of the 1914 war halted production. In 1909 however Sir Harry designed a two-stroke 3. 3 litre engine for his cousin Ralph Ricardo who had started a small concern, "a very amateurish one’ in a yard at Shoreham. This engine was used in the Dolphin car. ‘These cars were very well made and sold when it was discovered that the cost of building was far in excess of the selling price. " After this sharp lesson in applied economics the firm made two-strokes for the local fishing vessels and had partially retrieved their losses when Ralph Ricardo departed to a post in India in 1911. Sir Harry continued to design engines under a licensing agreement with the Britannia Co. of Colchester. and with Messrs. Browett Lindley of Manchester in the field of small electric lighting sets. For the firms concerned the engines proved commercially advantageous and several hundreds were made up till 1914. "In all cases I acted as designer and consulting engineer, but in an honorary capacity - for it was my spare time hobby. I did however receive some payment by way of royalties though these, I think, never amounted to more than 50 per annum.


"Early in 1915 I received a letter from Hopkinson, with whom I had rather lost touch for some years, saying that he had been appointed as Technical Director of the newly formed Air Ministry, that since our work together at Cambridge he had grown rather rusty on the subject of internal combustion engines and asking me to prepare for him a note setting forth my own views on the principal factors governing the design and performance of light, high-speed engines. This was a job after my own heart. Hopkinson was pleased with my effort, but to my horror had it copied and sent not only to some of the Technical Staff of the Ministry but also to the manufacturers of aero-engines, such as Rolls-Royce, Napier, Bristol and others. On hearing this I shook in my shoes expecting at any moment to be torn to pieces by outraged designers, but on the contrary I received the most cordial invitations from Royce, from Rowledge of Napier, from Fedden of Bristol and from the Royal Aircraft Establishment at Farnborough to visit them and discuss their designs. This was almost my first contact with any famous designers and was a turning point in my life. Almost over-night my status had changed from that of an unknown amateur pursuing an innocent hobby, to that of a serious person whose opinion carried weight."

Extract from "Horning Memorial Lecture, 1955" (Ref. 2)

Demonstration of the new Tanks

"I was invited to attend a demonstration of the new Tanks which was being held in a test ground close to Wolverhampton and which was attended also by various high-up officers in the War Office. A piece of waste land had been prepared to resemble as far as possible the typical fighting front in France which comprised trenches of various widths and depths, deep areas of barbed wire and other such-like obstacles. I was deeply impressed by what I saw of the ability of the Tanks to cross wide trenches, to dig themselves out of deep shell holes and to deal with the barbed wire, either by trampling it underfoot or by sweeping it with grappling irons. The military authorities also appeared to be rather impressed but they maintained that the only test that would really convince them were tests carried out against the enemy in France, and they insisted that a certain number of the Tanks should be despatched to France as quickly as possible. Accordingly a about twenty or thirty of the Tanks were manned by crews recruited from Squadron 20 and despatched to France and almost immediately were put into action on a sector of the front which was then comparatively quiet, and not very heavily manned by either side. The whole operation was a tragic example of mismanagement, muddle and misunderstanding. Without any preliminary rehearsals, and without any clear plans for co-operation with the infantry, who apparently were as ignorant of their purpose as the enemy, the Tanks were apparently instructed to cross no-man’s land knocking out any machine-gun posts on the way, to get astride the enemy’s first line trench, and then to carry on as seemed best to them. The Tanks had no difficulty whatever in crossing no-man’s land, and after knocking out a number of machine-gun posts on the way they arrived successfully in the enemy’s front line trench, only to find, to their dismay, that no infantry were following them, and that they were left alone to their own devices. Most of them having no idea what to do next returned to their base but several carried on straight ahead, crossing the enemy’s second and third lines of entrenchment, and so out into the open country behind the enemy’s lines, only to run out of petrol. They did what they could to wreck their machines and then abandoned them and attempted to escape back to our lines. Most of them were captured but a few did succeed, during the following night, in getting back to our side. The whole affair was really a disaster of the first magnitude, for the Germans now knew what to expect and had ample time to prepare counter measures in the form of light anti-tank guns, rifles with armour-piercing bullets, land mines and other obstacles, while we on our side had little or no hope of producing more Tanks for at least twelve months. This at least is the unhappy story brought home by the survivors. It may have been highly coloured, but they were feeling bitter and frustrated, but it could not have been far from the truth. On the credit side the military authorities could not ignore the fact that a handful of men and a very small number of Tanks had been able to break clear through the German defensive lines, and on the strength of this achievement, orders were given that the production of Tanks should proceed on a large scale.

It was relatively easy to screen the tanks from aerial observation even when close behind the front line, but all camouflage would be useless in the face of exhaust smoke (which was plentiful in the existing sleeve valve Daimler engines). It seemed that all the automobile manufacturers already had their hands full, either with military vehicles or with aircraft engines which at that time had first priority. It was apparent, therefore, that an entirely new engine would have to be designed and built. Through my grandfather firm I was in touch with a number of the manufacturers of large industrial engines, such as Mirrlees, Crossley and others, and I was asked to canvass these to find out whether they had the capacity and were willing to tackle the construction of such an engine. I found them riot only willing hut eager to do this, but not to tackle the design, which they said was quite outside their range of experience. I reported this to Tennyson d’Eyncourt who replied: "You seem to have a pretty good idea of what is required. Will you undertake it? I told him that although I had always been deeply interested in engine design, my experience was really very limited, but I should love to have a try at it provided that I could be assured of the good-will and co-operation of the would-be manufacturers, but that I was afraid that the engineers of such firms with a hundred times my experience would regard it as an impertinence to be asked to build an engine designed by a little-known young man."

I had, of course, already given a great deal of thought to this problem of an engine for the Tanks, and had already formulated fairly clear ideas of my own as to how it should be designed. It was left that I should go home, prepare notes on my views together with a rough scheme design of the kind of engine I had in mind. This done he would call a meeting of the would-be constructors at which he himself would take the Chair, and we should discuss the design and my notes. If the reaction was favourable then we should go ahead with all speed.

The meeting, held about a week later, was a great success. Sir Eustace handled it admirably. My notes and my proposed design were very well received, in fact they were all very flattering about it. Sir Eustace impressed upon them the need for urgency, and pointed out that I would be in need of and would welcome all the help and advice they could give me.

From Unpublished Technical Note by Sir Harry

Technical Problems: 'The Barking Dog'

On occasions one or more of the cylinders would give out a loud noise, very much resembling the bark of a dog, and loud enough to be really alarming. None of us, nor anyone else I consulted with, had ever come across the like of it before, and for a time we were completely puzzled. Its onset would appear to be completely erratic. It would occur for two or three, or perhaps more, consecutive cycles in one cylinder and then not again for hours. It was one of those tiresome troubles where one could not reproduce the phenomenon one wanted to examine. Windeler suggested that it might be piston blow-by. We therefore removed the gauze screens from the intakes side of the crosshead chambers, and this enabled us with the help of a mirror to see the underside of the pistons while running. When at last we happened to be looking at the right moment we could see a shower of sparks coming down apparently all round the piston. This confirmed that it was blow-by - but why? On lifting the cylinder the piston appeared to be in perfect condition. The rings were all free and in good order. I should perhaps explain that at this time the aluminium piston was a novelty with which very little experience had yet been gained. I had used it on my own experimental engine but had never encountered "barking dog".

I had sought the advice of an aluminium foundry who were supplying pistons to Rolls-Royce. They recommended a copper alloy, I think 12% copper. This, they said, had good bearing properties, machined easily and could be sand or die cast. They pointed out, however, that it was a very soft material and if the piston rings had much side clearance they would probably hammer down the lands. They recommended, therefore, that the rings should be fitted with the absolute minimum of working clearance and this had been specified on the drawings. In the course of discussions it was suggested that the phenomenon of "barking dog" was due to collapse of the rings for lack of a sufficiently rapid build up of pressure in the groove behind the ring. This, at least, seemed a plausible explanation and I tried the experiment on one piston of venting the groove for the top piston ring to allow a free escape of any gas that reached the ring groove. The result was very striking. The piston to which it had been done barked violently at every cycle and all the time. After a short run we lifted the cylinder and found the top ring broken in at least a dozen places. This experiment seemed fairly conclusive evidence that the trouble was collapse of the rings due to failure of gas pressure behind them. My next experiment was to file a number of small radial grooves in the top face of the piston ring. This was effective but the objection was raised that there was nothing to prevent the ring being put in position upside down after an engine overhaul. Nevertheless, the first batch of engines were all sent out with rings grooved in the manner I have described, and no case of "barking dog" was ever reported. Text 9

On the engines set aside for endurance running we tried the pistons with two or three thousandths clearance in the ring groove, and had no instance of "barking dog" with this arrangement, nor was there any appreciable wear of the ring lands, and so in all future engines the rings were given a liberal side clearance and no further trouble occurred on that score. The prevalence of 'barking dog' was the most alarming of the teething troubles we had to face. Fortunately the cure was found before any of the engines went into service.

From Unpublished Technical Note by Sir Harry

Versatility of the Ricardo Tank Engine

"I have said that the number of engines for Tanks turned out during the years 1917-18 were considerably greater than the number of hulls. These engines were in great demand for a large number of other purposes. Several hundred of the 150 H.P. engines were used in France for providing power and light to base workshops, hospitals, camps, etc. These engines in many cases were called upon to run for very long spells, sometimes non-stop for several weeks on end. This, of course, was a far more arduous duty that service in the Tanks. Others were in demand for the Navy for the propulsion of all kinds of auxiliary craft. Others yet again were used in improvised shunting locomotives. The Navy, however, preferred the larger 225 H.P. engine which was uprated to 260 H.P.

Looking back I think that the success of these engines was due very largely to the use of the crosshead piston. In general the piston is one of the most vulnerable parts of any internal combustion engine, but in the case of the crosshead piston, thanks to the very efficient air cooling and to its separate system of lubrication, the pistons themselves were virtually quite trouble-free. Once we had nailed down and cured the "barking dog" trouble, we never had the slightest trouble with the pistons. We never suffered from stuck rings or packed out piston rings. We had no means in those days of measuring piston temperatures, but from a casual glance it was obvious that they were running very cool indeed. Somewhat approximate measurements of the amount of heat removed from the pistons by the high velocity air circulation under the crown showed that on the 150 H. P. six-cylinder engine we were removing heat at the rate of somewhere between 150 and 200 B. T. Us per minute. This represented rather more heat than we needed to overcome the latent heat of evaporation of the fuel, but in view of the very poor volatility of the fuel we had to use, it was perhaps just as well. In both the 150 and 225 H. P. engines the specific output was slightly over 1 H. P. per sq. in. of piston area at the normal governed speed and rating. This of course is not a very high specific output in terms of today, but the pistons were relatively large. Those of the 225 H. P. engine were 6 in diameter and the H. P. per piston was rather over 40. Apart from the excellent behaviour of the pistons as such, the absence of any transmission of heat from the piston to the crankcase was a tremendous advantage, as also the absence of any contamination by combustion products passing the piston. Lubrication of the pistons was always under complete control while the oil in the crankcase remained cool and clean.

To sum up, I think the great success of the Tank engine, of which probably only about 75% were installed in Tanks. stemmed largely from the fact that they were by far the most powerful petrol engines apart from aviation engines available to the allies. It stemmed also, and above all I think, from the generous help and wonderful co-operation on the part of everyone concerned."

From Unpublished Technical Note by Sir Harry

THE TANK – Historical Note by K.A. Knell

In the 1914-18 War once the fronts were stabilised the odds were all on the defending side. While the machine-gun dominated the battlefield, no frontal assault had much chance, and no flank attack was possible because the Western Front had no flanks.

Attacks were ordered and made with appalling cost in human lives: during the great British offensive at the Battle of the Somme, for example, 60, 000 British troops were lost on the first day. After four months of continuous offensive we lost 420,000 killed and wounded for the gain of seven miles. Another 300, 000 men were lost at Passchendaele. During the French attacks of 1917 the results were the same and the German Army’s last supreme efforts - in March 1918 - were held by the British.

What might have been completely deadlock was finally broken by the extensive use of the tank. The Germans had turned to chemistry in the form of poisoned gas - the British experimented unsuccessfully with gas and turned to the i.c. engine. The British tank was first used in small numbers at the Battle of the Somme, as has been described elsewhere. Although not used in large enough numbers to affect the outcome of this Battle, their initial successes were such as to convince some people that if used in sufficient quantities their help could be decisive.

The turn of the tide came in July 1918. Ludendorff’s knock-out blow against the British in March had failed, but he still had mighty forces. He delivered further attacks against the Allies in April and May. His fourth offensive had just begun on July 18 when General Foch hit back. The French attacked with a force of light tanks leading the way and broke the German line.

Another outstanding Allied success was the British attack near Amiens on August 8th. This attack started with a massive onslaught by 456 tanks. Canadian. Australian and U.K. troops followed, helped by armoured cars, and stormed and broke the German lines. By the end of the first day 16, 000 prisoners had been taken. ‘August 8’ wrote Ludendorff afterwards, ‘was the German Army’s black day.’

The great European armies of the day, traditionally composed of peasants officered by the often inept aristocracy, were finally to be conquered with the help of a new breed of men - the technologists and the technicians. A lesson, that we, the demonstrators, did not finally absorb until 1940!


"Since the earliest days of the gas engine the advantage of working with a large excess of air and therefore at a lower cycle temperature has of course been well recognised, and the gain in thermodynamic efficiency from the reduction not only of direct heat losses but also of dissociation and that due to the changed specific heat of air at high temperatures has been well understood and evaluated. It is small wonder therefore that the lures of operating with a stratified charge should have attracted scores of inventors ever since the end of the last century, but despite extravagant claims to the contrary nobody yet has achieved any measure sure of success as applied to road service, which requires that it must apply to the entire range of torque from idling to maximum and that with repeated jumps from one extreme to the other at frequent intervals.

During my latter school days making use of a piston connecting rod and crankshaft from a discarded gas engine, I had built up a very crude single cylinder unit embodying a conical combustion chamber with the sparking plug at the apex and two inclined valves operated by long pushrods from two crankshafts mounted on the bedplate. Incidentally, this engine still exists at Shoreham, and Major Evans resurrected it as an exhibit at one of our Flower Shows. I had intended to employ it for pumping water at a new house, which my father was planning to build at Graffham.

Later when as an undergraduate at Cambridge I assisted Prof. Hopkinson with his research work, I told him of what I had done and of the difficulties I had encountered; he pointed out that these were probably due to the narrow range of burning of petrol air mixtures. In the labs at Cambridge we had several large steel bombs in which Ewing had previously carried out a number of experiments with various gases including hydrogen in order to determine the rate of flame propagation and the range of burning. We repeated his tests using petrol air mixtures, both under stagnant and highly turbulent conditions. As compared with Cambridge town gas we found the range of burning of petrol to be considerably narrower, and slightly narrower still under conditions of high turbulence. On the evidence of these tests he was somewhat surprised that I had been able to obtain reasonably complete combustion with so weak a mean mixture strength in the main combustion chamber.

While at Cambridge I had become very keen on the two-stroke cycle and sought to apply the experience I had gained to a two-cycle engine; this engine (which later became known as the ‘Dolphin’) used a separate pumping cylinder fed by a conventional carburettor delivering to the working cylinder through an automatic inlet valve at the top while the exhaust was through ports uncovered by the piston towards the end of its stroke. In this engine the inlet valve opened into a bulb in which the sparking plug was fitted and then through a restricted neck opening out into a deep conical combustion chamber; by this arrangement I sought to kill two birds with one stone, to achieve good scavenging and a minimum loss of fuel through the exhaust ports by bringing the scavenging charge into a solid stream before its entry into the main combustion chamber, and at the same time leaving the small bulb full of combustible mixture uncontaminated by exhaust. In this engine I employed a homogeneous charge of constant mixture strength controlled in the usual manner by a throttle valve on the intake to the pumping cylinder. In this engine I was employing a different line of approach for I was seeking to get the best possible measure of stratification as between a combustible charge and the hot residual excess gases, while the relatively pure mixture retained in the bulb and around the sparking plug allowed of excellent idling. In the design of this engine I enjoyed the excellent advice given me by both Hopkinson and Dykes at Cambridge.

All this was nearly 60 years ago but no change has occurred during the intervening years in the range of burning of volatile hydrocarbon fuels. To be of any use for automobile service with its rapid alterations of load from one extreme to the other nothing less than complete stratification over the whole range of load will suffice."

From Unpublished Technical Note by Sir Harry


One of the most famous of all Triumphs was the "Riccy" The engine was designed by that well-known authority on internal combustion engines, H. R. Ricardo (now Sir Harry Ricardo) - whence the name "Riccy" - and was, therefore, of very advanced design; there were several features which at that time, 1921, were startling novelties.

The cylinder barrel was of steel, spigotted into the cast-iron head, which was held down by five studs on to a metal to metal ground joint. There were four valves, two inlet and two exhaust, with a 90 degs. angle between the pairs, and the inlet valves were masked, the first application of this feature to a motor-cycle engine. The bore and stroke of the engine were 80.5 and 98 mm respectively, and unlike other designs the piston was not full skirted but of the now very popular slipper type.

Ricardo modified the engine in several details for 1922. The bore and stroke were altered to 85 and 88 mm. respectively, allowing a 25 per cent, increase in valve area. The valve gear was stiffened, the exhaust ports lay at an angle to each other instead of parallel as before, and dry-sump lubrication replaced the total loss system, a double piston oscillating pump delivering oil under pressure to the big-end and scavenging the sump. Major H. B. Halford spent some time at Brooklands with an experimental machine which differed from the other design in one very important respect, the cylinder head was water cooled; the radiator was carried in the front part of the petrol tank. It was decided that the advantages of water cooling were not sufficiently great to justify the extra complication and the experimental head was abandoned.

In the Senior T.T. of 1921 a "Riccy" lay sixth for four laps, then slowed but finished. In other events these models were more successful, finishing 3rd in the 500 c.c. class of the Brooklands 500-mile race and the French G. P., capturing the 500 c.c. hour record, and taking the mile record flying start, at over eighty. With the improved engine, but handicapped by the loss of second gear, Walter Brandish finished 2nd in the Senior T.T. of 1922 at 56.22 m.p.h.

From: "Britain’s Racing Motor-Cycles" by L. R. Higgins. Foulis 1953.


One of the great contributions made by Ricardo to the internal combustion engine industry has been his development of the understanding of the phenomena controlling combustion in both the spark ignition engine and in the diesel engine. On the one hand he was one of the first to understand the part played by turbulence and the true nature of detonation; on the other his knowledge of the necessity for ordered relative air/fuel motion made possible the transition of the diesel from an engine akin to the reciprocating steam engine in size, weight, and speed to the small, compact units of today. Three notable advances in combustion chamber design are shewn below:

(a) The turbulent head (1919) for petrol engines. Ricardo realised that turbulence increased flame speed and achieved this by offsetting the cylinder head. He also recognised that it was the absolute distance travelled by the flame that increased the tendency to detonate so the chamber was made as compact as possible. Previous practice was to use a slab-like chamber as in (b)

(c) The induction swirl chamber. This represents one of the earliest attempts to achieve orderly air motion in a diesel engine, the swirl being initiated by inclined ports and accentuated by forcing the air into a small cylindrical volume

(d) The Comet Mark III compression swirl chamber. The most famous of all diesel combustion chambers, this design embodied intense swirl with a reasonable rate of pressure rise and good fuel consumption. In its latest form it is still one of the most widely used chambers when, power rather than economy, is the prime consideration. It was the subject of a lengthy legal battle about infringement of Patent rights between Riccardo’s and Rootes’ Bros. won by Ricardo’s who were represented by a young lawyer named Stafford Cripps (later to become Chancellor of the Exchequer).


E-35 Variable Compression Ratio Engine

This was the first variable compression engine designed by Sir Harry. On it much early classical work on the characteristics of (then) unknown hydrocarbons was undertaken and the concept of Highest Useful Compression Ratio derived.

"During the 1914-18 War, I came into contact with Sir Robert Waley-Cohen, of the Shell Company, who, at that time, was chairman of a committee dealing with fuel supplies. To him I told of my experiments on detonation, of the very great importance I attached to it, and of my belief that it was largely a function of the fuel. He immediately sent me samples of a wide range of fuels of different origin, which I tried out on my supercharging engine, and I was able to show him very great differences in their behaviour as regards detonation. Of these sample fuels, by far the best was one hailing from Borneo. He told me to my amazement, that hundreds of thousands of tons of this particular petrol were being burnt to waste in the Borneo jungle merely because it did not comply with the existing specification as to specific gravity. On the strength of these observations, he invited me to undertake, as soon as the war was over, a comprehensive research into the behaviour of liquid fuels. This, then, formed the first piece of large-scale research undertaken at our new laboratory at Shoreham."

Extract from "Presidential Address" (Ref. 1)


"About this time I had became very interested in aero-engines and built myself an experimental four-cycle engine with variable supercharge, with the object of maintaining ground-level power at high altitudes. This took about two years of spare time to make; it worked quite well, but in those days. I failed to rouse any interest in it, for I was met by the reply that aeroplanes would never fly high enough to need supercharging."

Extract from "Presidential Address" (Ref. 1) 

Sleeve Valve Aero Engines

E-25 Single sleeve valve single cylinder research engine. This engine carried a load of 520 lb per sq. in. B. M. E. P. when engaged in supercharging tests in the 1930s. From this kind of work was evolved the successful sleeve valve aircraft engines which alone among the belligerents the British used. The Perseus, Hercules, Taurus, Centaurus from Bristols, the Rolls-Royce Eagle, and the Napier Sabre produced 200, 000, 000 H. P. during the war years. In fact the Rolls-Royce Merlin and Griffon were the only common British poppet valve aircraft engines by 1945.

As a result of the considerable amount of development work which Ricardo’s carried out on the sleeve valve engine this became a widely used form of construction for high powered British aircraft engines built during and after the 1939-45 War. Some 130, 000 were built by leading aero-engine manufacturers of which the  examples illustrated are best known.


From the 1930s onwards Ricardo petrol and diesel engines were developed to power various makes of car including Bentley, Citroen and Peugeot. In 1951 Ricardo & Co. acted as consultants on the ‘FELL’ diesel-mechanical locomotive.


Ricardo & Co were also active in developing a range of compressors for various purposes. These included a special type of oxygen compressor made in some quantity for the Admirality. Highly compressed oxygen will react with lubricating oil to form an explosive mixture. This reciprocating compressor was designed to have water lubrication. Great care was paid to the tolerances and to the choice of materials.


Ricardo's Steam Engine, 1951. (This engine was a twin)

"It was built in conjunction with the National Research and Development Corporation (the purpose of which is to finance likely inventions) with a view, to selling it on the Indian market. The idea was that the Indian village community should have some other source of power than bullocks, and this engine had a boiler which could burn any fuel including brushwood and camel dung. The scheme was not a success partly because the engine is still too elaborate, partly because oil engines are at least as convenient, and partly because the conservatism of the Indian village was underestimated."

Critics commented to Sir Harry that it was unusual for him to be interested in steam, after his reputation in the internal combustion engine world. He replied that his first love was steam; a remark born out by the paragraphs below extracted from his Presidential Address (Ref. 1)

"As a child, I was always fascinated by engines and mechanical motions generally, and above all, by the great mystery as to how such things were actually made. The romantic side had also a strong appeal and I can well remember and even still feel the emotional thrill of watching a great steam engine with its gleaming muscles, its rythmic breathing and its unhurried dignity. In those days, one of my greatest delights was to be allowed to go to the Gray’s Inn Road where, behind a tiny shop window, sat an old man working on a very crude and primitive metal lathe. Looking back over the years, I think that that old man was the finest skilled craftsman I have ever met, for there seemed literally nothing he could not make on that ramshackle lathe without even a slide rest. One red-letter day, after seeing my face glued to his window, he invited me in, and thereafter it was my delight to sit by him at work. He showed me how to make drills out of odd bits of piano wire, how to harden and temper them to suit the material he was about to drill, how to make turning tools out of old files, how to solder and to braze, how to cut screw threads with a chaser, by sheer sleight of hand - an art I have never succeeded in mastering - and in short, how to tackle almost any job. Needless to say, after each visit, I returned home clamouring for a metal lathe of my own and, being a spoilt child, I soon got one - a screw cutting lathe, with a compound slide rest. With this I tried to emulate my old mentor in the Gray’s Inn Road, and, thanks to his coaching, I soon became reasonably adept. In those days, it was the summit of my ambition to make a working model steam engine, and, at the age of twelve, I was given a set of castings of a vertical double-acting steam engine, but the task proved too difficult for me and it was never completed. I next tried myself to design a single-acting steam engine of easier construction within my limited skill as a machinist. This was a success in so far as it actually worked and I shall never forget the proud moment when at last it continued to turn on its own without any assistance from my finger on the flywheel. Needless to say, both the design and construction were very crude, but I had achieved my first ambition of making an engine which worked by itself. As my skill as a mechanic improved, so my designs became more ambitious and I made several more engines, some of which were quite reasonably efficient.

I have dwelt on these childish experiences because looking back, I think I learnt more of actual value from these early and very crude attempts at design and manufacture than from anything else.

My crowning achievement at school was the conversion of my push bicycle to motor cycle by the addition of a home-made two-cylinder uniflow steam engine and a coal-fired fire-tube boiler, made of very thin copper reinforced with wire winding. This rather absurd machine caused a good deal of amusement generally, but some anxiety to my poor house-master, who never expected it would materialize and was convinced that it would blow up, as well it might have done."

Extract from "Presidential Address" (Ref. 1)


To those of you who are about to carry out research of the kind I have been involved in, I would like to utter a few words of advice and a few warnings. First and foremost, make up your mind what to go for, that is to say what, in your judgement, will be likely to fulfil a need in say two or three years’ time; having once decided, keep that objective always clearly in view and do not, on any account, allow yourself to be side-tracked from it. Do not let yourself be too cast down by disappointment, or too elated by those initial successes, which so often prove to be only transitory. Do not be afraid of failures - here I speak with experience, for I have been responsible for many. One learns as much, or possibly more, from one’s failures as from one’s successes; the downright failure is always instructive, and is usually fairly early apparent before it has cost an undue amount of time or money. The real danger, and by far the most difficult to cope with is the partial success, the achievement which is either just not quite good enough, or for which the need is passing. To cope with this taxes one’s judgement to the limit. It requires all one’s strength of mind to break off, when cool judgement counsels the abandonment of a project to which one has grown very attached and on which one has lavished years of thought and painstaking research; but such decisions have sometimes to be made and, speaking for myself, I find it easiest when the demon of doubt becomes insistent, to suspend all work and thought on the project for a few days or weeks and then review it afresh. It is surprising how coldly and dispassionately one can review and, if necessary, reject one’s own most cherished schemes after they have been banished from one’s mind for a decent interval.

Extract from "Presidential Address" (Ref. 1)


In his book, Science in Writing, T.R. Henn discusses the gap between writing as practised in the Arts and in the Sciences. He deplores the obscure and deliberate cultivation of a mystery and encourages a return to clarity and simplicity. He provides extracts from great scientific writers from Francis Bacon to Max Born. C.f. Sir Harry Ricardo’s works (the passage exemplified is a discussion on the Design of Bearings and Crankshafts — The High Speed Internal Combustion Engine, Pt. II, 1953 edition) he says:

Nearly all constructions involve in their design a number of compromises between the form desired, the materials of which it is made, and the conditions under which it is to operate. The design of a ship’s hull is an excellent example. To arrive at a compromise involves the orderly assessment of qualities and conditions; at first singly, and then in combination; weighing and balancing each in a system of values; making judgements one against the other, keeping always in mind the overriding considerations of the object to be attained.

Sir Harry Ricardo is one of the greatest authorities on the high-speed internal-combustion engine, and has given his name to various aspects of its design. Here he is considering two of its most important components. Description of qualities is followed by analysis and selection. The prose structure, which is beautifully clear and simple, follows with great precision the demands of the differing statements. There is no ‘normal’ paragraph length; it may be short or long as the contours of the thought require. Imagery is used sparingly; the only notable one is the comparison of the bearing to a sponge, perhaps the last comparison that would have occurred to a non-engineer.

The whole is an excellent example of descriptive writing, which does not need the assistance of diagrams; it is perhaps a tribute to one quality of the prose that no notes appeared to be necessary. The numbering of sub-paragraphs for the sake of clarity is a perfectly legitimate device, and the student of prose might well study the various possible systems for doing this.

Cambridge University Engineering Department 2000